Rheostat



July 21, 1959 M. J. MGCABE 2,896,184

Rmaos'mA Filed Nov. 20, 1957 l 2m (27 v 27 265 25 VZ 'Wr/25 fa a L-1. 271% 2 2; v, 21 -r M ,i K :73\ if" I 26" 171.4, i 1m i 1 @25W 20 Jaa fad, 19 )IIL *J0 17 I /75 11| 32 'Lff L? 26 l 4 I 2b f77/5y l I |||l Z6 1J i if lm1 10b .95 l E /fa l j7/ M5 Jaa :di M HH 17a f2 (Jac y I'VENTOR. J5 Y Muff/26W J Mc Calbe f l BY United States Patent RHEOSTAT Matthew J. McCabe, Bristol, Conn., -assignor to The Superior Electric Co., Bristol, Conn., a corporation of Connecticut Application November 20, 1957, Serial No. 697,643

3 Claims. (Cl. 338-97) This invention relates to rheostats, and more particularly to improvements in the kind in which the ohmic resistance of a pair of resistance wires is variable by the operation of a sliding contact member or bridge placed conductively across the wires.

One object is to provide an improved rheostat unit in which the adjustment of the resistance is by the rotation of a contact-carrying operative shaft, and which is compact, simple, as well as inexpensive to manufacture in quantity, and which is rugged, durable, as well as precise and smooth to manipulate, and which is readily mountable on a chassis for operation.

In attaining these objects the invention provides a rheostat which has a disc-shaped insulator body having a narrow cylindrical surface with a pair of resistance wires encircling and engaging the cylindrical surface of the body and running parallel to each other. The insulator body is molded around one end portion of a coaxial mounting sleeve to constitute therewith a composite rigid member with an axial bore, the mounting sleeve being adapted for rigid fastening to a chassis. A rotary insulator arm coaxial with and close to the insulator body has cooperative engagement with the resistance wires through a resilient contact member carried by the arm and overlying the periphery of the body. The insulator arm is molded around one end of an operating shaft constituting therewith a composite rigid operating member. The shaft extends through the mounting `sleeve and is rotatable from the outer end thereof. This organization of the parts provides effective guidance for the shaft in the sleeve which absorbs substantial contact pressure reaction force exerted upon the arm, and results in smooth and easy operation of the shaft.

In the preferred form of the invention, the resistance wires are in the form of a single length of wire looped around an anchoring screw which is threaded radially into the insulator body at a point of its periphery adjacent to the terminals of the wire. Tightening of the anchoring screw will tension the two parallel portions or sections of the resistance wire around the cylindrical face of the insulator body.

Other features and advantages will hereinafter appear.

In the drawings:

Figure 1 is a longitudinal part-sectional 'view of the rheostat, illustrating the composite structure of the parts, as well as the mounting of the rheostat on a chassis.

Fig. 2 is an end View of the rheostat taken on line 2-2 of Fig. 1, with the insulator arm partially broken away to expose the spring washer associated therewith.

Fig. 3 is a top View taken at an angle on line 3--3 of Fig. 2 showing particularly the location of the wire terminals and of the wire anchoring screw.

Fig. 4 is a bottom view of the rheostat taken on line 4-4 of Fig. 2.

Referring to the accompanying drawings, the rheostat illustrative of this invention comprises a disc-shaped insulator body of molded plastic composition having a narrow cylindrical face 10a and parallel end faces 10b Patented July 21, 1959 ice and 10c. The insulator body is molded around one end portion of a mounting sleeve 11 so as to constitute therewith a rigid composite member, the sleeve being formed with an intermediate collar 12 constituting a shoulder for the end face 10c of the body. The mounting sleeve has an -outer threaded end portion 13 carrying a pair of lock nuts 14 and 15 whereby the sleeve may be held rigidly connected to a chassis as is indicated by a wall portion 16 thereof through which the mounting sleeve extends and against which the lock nuts are tightened from each side thereof.

A single length of resistance wire 17 has its ends fixed to a pair of terminals 18 and 19 which are juxtaposed to one another extending radially from the cylindrical surface of the body. The resistance wire is looped around an anchoring screw 20 threaded radially into the body at a point adjacent to the terminals, thus constituting a pair of parallel wire sectionsr17a and 17b tensioned on the body along' the periphery thereof by the tightening of the `screw as is most clearly shown in Figs. 2 and 3. Fig. 2 in particular shows the iiat head 21 of the screw in a recess 21a formedin the cylindrical face of the insulator body and the wire looped around the conical underside of the head and drawn down into the recess by the tightening of the screw with the top face of the screw then substantially flush with the surface of the body. In the preferred form each of the two terminals 18 and 19 is in the shape of a pin molded radially into the body 10, having a reduced stem portion 22 intermediate a foot portion or collar 23 and a flat head portion 24. The foot portion 23 has a transverse bore 23a indicated in dotted lines in Fig. 3, having one end of the wire threaded therethrough terminating in a hook portion 17C and secured in place by soldering.

A contact member 25 or brush in the form of a flat spring having a pair of parallel resilient contact lingers 25a and 25b in sliding contact with respective wire sections 17a and 17b, is carried by an angular insulator arm 26 rotatable coaxially with respect to the insulator body and extending in close proximity thereto. The arm has a transverse end portion 26a at the outer end overlying the periphery of the insulator body, with the contact member 25 fastened to the inner face thereof as is indicated by a pair of fastening rivets 27.

The arm 26 of a plastic composition is molded around one end portion of an operating shaft 28 to constitute therewith a composite rigid member. The shaft is rotatable in the mounting sleeve 11 and has ample guidance along the length thereof. An outer end portion 29 of the shaft projects from the outer end of the mounting sleeve and carries securing means to prevent any substantial axial displacement of the shaft in the sleeve, provided preferably in the form of a snap ring 31 in a peripheral groove on the end portion 29 of the shaft. A spring washer 32 upon the shaft is interposed between the insulator body and the arm for eliminating any axial play between the shaft and the sleeve. The washer is exemplified as having a plurality of pairs of peripherally extending resilient tongues, the tongues 32a and 32b of each pair extending opposite to one another.

A lug 33 is formed integral with the insulator body to provide stop means which define the extreme rotational end positions of the arm 26.

After the rheostat is thus assembled as a compact unit, it may be mounted upon a chassis as by means of the lock nuts in the manner clearly shown in Fig. 1.

It will be seen that the rheostat of this invention comprising a pair of coaxial cooperative rigid composite members, presents a compact serviceable unit simple to manufacture and to assemble, with the arm and shaft as a rigid member guided in the mounting sleeve which readily absorbs the reaction force imposed upon it by the con- 3 tact pressure between the contact member and the wire. A removable operating knob or other operating member may be attached to the free end 29 of the operating shaft.

Variations and modificationsmayibe'madewithin thev j scope o'f'the claims and 'portions 'of vthe improvements may' be used without others.

lclaim:

Y1. A rheostata'dapted .to be mounted upon 'a chassis comprising Yan -elongate mounting sleeve, an Yinsulating body molded on one end portion ofsaidsleeveto beV rigid therewith and'having a narrow cylindrical peripheralsurface, said sleevetbeing longerlthan the 'thicknessOfthe insulatingbody andprojecting `outwardlytherefrom1 'a' pair of juxtaposed terminals carried by the body atthe'perip'h ery thereof, an anchoxingscrew 'threaded' radially-into`the perifvhery ofthebody spaced fromsaid terminals, =a resistance wire having its ends vconnected'to 'respective terminals andthe wire`looped`around said anchoring screw to constitute a pair of parallelwire sections lyingon/and held stretched along the periphery of the body by the screw when tightened, Aan operating shaft extending through said 'mounting sleeve -to project 'from both sides of the .sleeve Vand retained therein against substantial axial displacement, said vsleeve constituting an elongatebearingforsaid shaft, an arm of insulating 'ma- "beyondthesleeveto'be rigid'therewithfor'rotationtherewith, said arm extending radially from said shaft in close proximity to said body and overlying the periphery of the body, a bridging contact carried directly by said arm and extending across both said parallel wire sections and normally biased into sliding teont'act therewith incident to rotation of said shaft and of said arm carried thereby.

2. The rheostat according to'elaim 1, wherein said terminals are I.in vthe form aof apins extending radially .from said insulator body, each pin fhaving Sa transverse v1.1016 through which an end portion of the resistance wire extends. the wire vterminating ina hook portion extending around the outside 'offthe pin and 'securedthereto 3. The rheostat accordingvto .claim 1, wherein said insulator body has a stop formed integral therewith positioned for engagement with and limiting the rotary movements of the contact carrying arm.

RefereneesCitedin'-thele 'of this `patent UNITED STATES 'PATENTS lPuerner -umu Apr. 29, I1-952 

